In recent years, the wind tunnel testing of airplane models has involved the increasing use of turbopowered simulators to simulate the fan-jet engines commonly utilized on actual airplanes. These turbopowered simulators are of the general type shown in the Kutney and Erwin U.S. Pat. No. 3,434,679. They may be generally described as miniature fan-jet engines, with the outstanding difference that they contain no "hot core" or gas producing section, but rather, are equipped with a turbine, powered by an external source of compressed air, which turbine drives the fan. Such simulators give the closest known practical model equivalent of real engines on a real airplane.
It is evident, however, that the accuracy of the prediction of full-scale operation on a real airplane depends upon the accuracy to which the characteristics of the simulator are known. Accuracy of prediction is not only highly desirable from an engineering standpoint, but from an economic view as well, for the reason that performance of airplanes is often guaranteed on the basis of model testing.